Depth and Refraction
Name: Vicky K.
A fellow teacher, who teaches physics to 16-18 year olds
has asked me to find out why at different depths the angle of refraction
in water changes. My immediate response was that it was because of a
change in density. Is this correct? If not what is the reason?
I was not aware that the angle of refraction in water changes appreciablywith depth, unless one is talking either about a change in salt content, if
in salt water, or temperature. The index of refraction of water [vs. air] at
14 C. is 1.33348 and at 40 C. is 1.33051.
For all practical pressures, the density of water is a constant, as is the
density of most other liquids.
You are correct. At greater depths, there are more molecules per unit
length to delay the light. As refraction is based upon speed of light
within the materials, the angle of refraction will vary with depth.
You are right. A change in density changes the index of refraction.
Density itself, however, can change as a result of pressure, temperature, and
impurity (e.g., salinity). Relative contribution of each to density change
can be calculated by determining the pressure, temperature, and the
composition of water at various depths of the ocean.
A quick look at the data tells me that:
A 1 degree change in temperature of water changes density by .01%
At a 1 km ocean depth, pressure of water is about 100 Atmospheres, and change
in density is about 0.5%
Salinity can vary quite a bit, and can affect density and thus the index of
Please look at this web site for more information:
Ali Khounsary, Ph.D.
Advanced Photon Source
Argonne National Laboratory
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Update: June 2012